There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

/pdf/light-emitting-diodes-ubzde6g9qc.pdf

Light-emitting diodes

Bridgeless power factor correction (PFC) converters are gaining popularity in recent years mainly for the efficiency superiority over their conventional topology counterparts. However, the quantitative reliability analysis of the bridgeless topologies in the wear-out region is missing and their reliability performances compared with the conventional one are unknown. Thus, based on the telecom applications with a representative mission profile in a rural area, this paper employs a mission profile-based reliability analysis approach to estimate the failure probability of an input-parallel output-series (IPOS) bridgeless boost PFC converter, along with the conventional one. Based on the measured efficiency data obtained from the built prototypes, the reliability analysis results indicate that under the same design specifications and criteria, the accumulated failure of the IPOS bridgeless is 0.27% within 20 years of operation, much lower than that (2.06%) of the conventional boost PFC converter.

Mission Profile Based Reliability Analysis of A Bridgeless Boost PFC

Solar PV panels are the center equipment of photovoltaic power systems. Condition monitoring is the key technique to predicting the health status and increasing the availability of PV panels. This paper proposes the Feature Fingerprint Intervals (FFI) method to monitor the degradation conditions of PV panels. The proposed approach is sensitive to the degradation mechanisms of PV panels. The prediction indicator, the amplitude of impedance spectroscopy, at FFI will be acquired directly from impedance spectroscopy while performing the online monitoring of PV panels. The health status of PV panels can be predicted based on the variation of the amplitude values of impedance spectroscopy at the FFI compared with the reference values. The proposed approach can support the accurate condition monitoring of PV panels.

An Online Degradation Condition Evaluation Method for Solar Photovoltaic Panels

In this article, authors propose a unified capacitors stress emulation method, which has two unique test capabilities: concurrent electrical stress emulation to ac capacitors and dc capacitors, and different electrical stress levels (including different ripple current, ripple voltage, and dc voltage) can be individually controlled for the testing samples. It preserves the advantages of a recently reported method with a minimum required power supply and is robust to testing sample degradation. This method is suitable for application-oriented stress emulation testing with different types of dc/ac capacitors and multiple electrical stresses in high-power converter systems. The circuit architecture and testing ability of this method are presented. Moreover, analytical models are derived to size the key components to realize various testing requirements. Proof-of-concept experimental results are presented to verify the feasibility of the proposed test method.

A Unified Capacitor Stress Emulation Method for High-Power Converter Applications

Junction temperature monitoring is crucial for the reliable operation of IGBT modules in many applications. The maximum collector current falling rate is an effective temperature-sensitive electrical parameter, which has good linearity and can be detected on-line. It has been reported that the parasitic inductance between the power and Kelvin emitter of IGBT modules can be used directly as the sensor for maximum collector current falling rate, nevertheless this method relies on the Kelvin structure and may introduce additional parasitic parameters. To solve this problem, the printed circuit board (PCB) Rogowski coil is proposed to measure the collector current falling rate, which has the advantage of contact-less and can be integrated with the driver circuit. In this paper, the temperature dependence of the maximum collector current falling rate and the measurement principle of Rogowski coil are analyzed. Moreover a double pulse test platform based on IGBT module is built to verify the effectiveness of the proposed method.

Huai Wang

Papers

Mission Profile Based Reliability Analysis of A Bridgeless Boost PFC

An Online Degradation Condition Evaluation Method for Solar Photovoltaic Panels

A Unified Capacitor Stress Emulation Method for High-Power Converter Applications

Measurement of Maximum $\mathrm{d}I_{C}/\mathrm{d}_{t}$ with Printed Circuit Board Rogowski Coil for Junction Temperature Estimation of IGBT Modules

An empirical model for thermal interface materials based on experimental characterizations under realistic conditions